Return the list of backup destinations with a Restic repository for the
current module.

Split the run_restic() function to ease custom subprocess invocation.

Run Restic backup faster with "--no-scan". This option avoid calculating
the backup size in advance. This is a time consuming operation,
unnecessary for a background job.

Add an optional "progress_callback" argument to agent.run_restic()
function, to provide UI feedback of Restic's progress.

Restic's output must switched to JSON format with "--json" argument.

Capture Restic progress during the restoration of a module instance.
Tune progress intervals of cluster/restore-module action.

While Restic backup is invoked in background most of times, the UI still
allows to run the backup immediately. In that case, a detailed backup
progress feedback is needed.

- Add fine-grained backup progess trace to module-backup command
- Run the backup from UI directly with module-backup command
- If module-backup runs interactively, skip progress calculation